Wireless communications links, using portions of the electromagnetic spectrum, are well known. Most such wireless communication at least in terms of data transmitted is one way, point to multi-point, which includes commercial radio and television. However there are many examples of point-to-point wireless communication. Mobile telephone systems that have recently become very popular are examples of low-data-rate, point-to-point communication. Microwave transmitters on telephone system trunk lines are another example of prior art, point-to-point wireless communication at much higher data rates. The prior art includes a few examples of point-to-point laser communication at infrared and visible wavelengths.
The need for faster (i, e., higher volume per unit time) information transmission is growing rapidly. Today and into the foreseeable future transmission of information is and will be digital with volume measured in bits per second. To transmit a typical telephone conversation digitally utilizes about 5,000 bits per second (5 Kbits per second). Typical personal computer modems connected to the Internet operate at, for example, 56 Kbits per second. Music can be transmitted point to point in real time with good quality using MP3 technology at digital data rates of 64 Kbits per second. Video can be transmitted in real time at data rates of about 5 million bits per second (5 Mbits per second). Broadcast quality video is typically at 45 or 90 Mbps. Companies (such as telephone and cable companies) providing point-to-point communication services build trunk lines to serve as parts of communication links for their point-to-point customers. These trunk lines typically carry hundreds or thousands of messages simultaneously using multiplexing techniques. Thus, high volume trunk lines must be able to transmit in the gigabit (billion bits, Gbits, per second) range. Most modern trunk lines utilize fiber optic lines. A typical fiber optic line can carry about 2 to 10 Gbits per second and many separate fibers can be included in a trunk line so that fiber optic trunk lines can be designed and constructed to carry any volume of information desired virtually without limit. However, the construction of fiber optic trunk lines is expensive (sometimes very expensive) and the design and the construction of these lines can often take many months especially if the route is over private property or produces environmental controversy. Often the expected revenue from the potential users of a particular trunk line under consideration does not justify the cost of the fiber optic trunk line. Digital microwave communication has been available since the mid-1970""s. Service in the 18-23 GHz radio spectrum is called xe2x80x9cshort-haul microwavexe2x80x9d providing point-to-point service operating between 2 and 7 miles and supporting between four to eight T1 links (each at 1.544 Mbps). Recently, microwave systems operation in the 11 to 38 Ghz band have reportably been designed to transmit at rates up to 155 Mbps (which is a standard transmit frequency known as xe2x80x9cOC-3 Standardxe2x80x9d) using high order modulation schemes.
Bandwidth-efficient modulation schemes allow, as a general rule, transmission of data at rates of 1 to 10 bits per Hz of available bandwidth in spectral ranges including radio wave lengths to microwave wavelengths. Data transmission requirements of 1 to tens of Gbps thus would require hundreds of MHz of available bandwidth for transmission. Equitable sharing of the frequency spectrum between radio, television, telephone, emergency services, military and other services typically limits specific frequency band allocations to about 10% fractional bandwidth (i.e., range of frequencies equal to about 10% of center frequency). AM radio, at almost 100% fractional bandwidth (550 to 1650 GHz) is an anomaly; FM radio, at 20% fractional bandwidth, is also atypical compared to more recent frequency allocations, which rarely exceed 10% fractional bandwidth.
Reliability typically required for wireless data transmission is very high, consistent with that required for hardwired links including fiber optics. Typical specifications for error rates are less than one bit in ten billion (10xe2x88x9210 bit-error rates), and link availability of 99.999% (5 minutes of down time per year). This necessitates all-weather link operability, in fog and snow, and at rain rates up to 100 mm/hour in many areas.
In conjunction with the above availability requirements, weather-related attenuation limits the useful range of wireless data transmission at all wavelengths shorter than the very long radio waves. Typical ranges in a heavy rainstorm for optical links (i.e., laser communication links) are 100 meters and for microwave links, 10,000 meters.
Atmospheric attenuation of electromagnetic radiation increases generally with frequency in the microwave and millimeter-wave bands. However, excitation of rotational transitions in oxygen and water vapor molecules absorbs radiation preferentially in bands near 60 and 118 GHz (oxygen) and near 23 and 183 GHz (water vapor). Rain, which attenuates through large-angle scattering, increases monotonically with frequency from 3 to nearly 200 GHz. At the higher, millimeter-wave frequencies, (i.e., 30 GHz to 300 GHz corresponding to wavelengths of 1.0 millimeter to 1.0 centimeter) where available bandwidth is highest, rain attenuation in very bad weather limits reliable wireless link performance to distances of 1 mile or less. At microwave frequencies near and below 10 GHz, link distances to 10 miles can be achieved even in heavy rain with high reliability, but the available bandwidth is much lower.
Much attention by the communication industry has been given recently to the challenge of providing equipment that will permit individual users to connect easily and inexpensively to high data rate communication links such as fiber optic trunk lines. This challenge is referred to as the xe2x80x9clast milexe2x80x9d challenge. Most individual electronic communication is via telephones through telephone lines in which pairs of copper wire connect the user""s telephone to a telephone company""s switching equipment. The circuit is basically the same two-wire circuit used by the Bell system since the 1890""s. This pair of wires may be (especially if the facility was built or updated relatively recently) a twisted pair. (Since multiple strands of twisted wire can be installed easily and inexpensively if installed when the premises is constructed, many premises are provided with several sets of twisted pairs running to various locations on the premises.) Typically, the telephone equipment at both ends of these telephone lines (i.e., at the user""s telephone and at the telephone company""s switching equipment) is analog and analog information is transmitted over this xe2x80x9clast milexe2x80x9d. This xe2x80x9clast milexe2x80x9d may be a few feet or many miles. These analog circuits cannot carry digital information since they were designed to carry voice. In these circuits the strength and frequency of the signal depend on the volume and the pitch of the sounds being sent. In order for computers to communicate using these lines the typical procedure is to convert the computer""s information into on and off analog tones that can be transmitted over the old fashion telephone circuit. This is done with a modem such as the Bell 103 modem that operated at a speed of 300 bits per second. More modern modems can transmit information in this manner at rates of 57,000 bits per second. The copper pair could be replaced with fiber optic lines or coaxial cable greatly increasing communication speed but to do this for thousands or millions of users would be extremely expensive.
A solution to this last-mile problem that is available in many cases is a technology recently developed which adapts the copper pair to transmit digital data. The line once converted is known as a Digital Subscriber Line (DSL). Typically a DSL access module is installed in the telephone company switching station which divides the available frequency spectrum on each telephone line reserving about 4 KHz of the lowest spectrum for existing analog telephone and FAX use. The remaining range of available frequency spectrum is devoted to digital data transmission. Typically, the systems are arranged so that much greater data rates are provided toward the user than from the user back to the telephone switching station. This type of service is called an Asynchronous Digital Subscriber Line (ADSL). With typical ADSL lines downstream data rates in the range of about 1.5 to 9 Mbps and upstream data rates of about 16 to 640 Kbps can be achieved. The possible data rate is largely dependent on the length of the pair of conductors with the limit being about 3.5 miles. Recently, technology has been developed for greatly increasing the potential data transmission rates using twisted pair links. Rates as high as 55 Mbps are possible. However, the technology works only at short distances such as less than about 1000 feet. Downstream speeds of 13 Mbps can be provided at distances in the range of up to 4,000 feet. For these Very high rate Digital Subscriber Line (VDSL) systems upstream rates of 1.6 to 2.3 Mbps are typical.
The term Ethernet refers to a family of local area network implementations that includes three principal categories that are governed by industry specifications to operate at data rates of: 10 Mbps, 100 Mbps and 1000 Mbps, respectively. These Ethernet implementations are well known and are described in many available network texts such as Internetworking Technologies Handbook, Second Edition, Published by Cisco Press, Macmillan Technical Publishing, Indianapolis, Ind., p. 87-124.
What is needed is a wireless data link that can provide trunk line data rates in excess of 1 Gbps over distances up to ten miles in all weather conditions except the most severe, with beam widths narrow enough so that an almost unlimited number of users can communicate using the same frequency bands combined with a network for dividing that data transmission capacity among many users to so that each of the users can have available to him at high digital data rates.
The present invention provides a point-to-point, wireless, millimeter wave trunk line communications link at high data rates in excess of 1 Gbps and at ranges of several miles during normal weather conditions. This link is combined with an Ethernet network to provide high speed digital data communication among a large number of users. In a preferred embodiment a trunk line communication link operates within the 92 to 95 GHz portion of the millimeter spectrum. A first transceiver transmits at a first bandwidth and receives at a second bandwidth both within the above spectral range. A second transceiver transmits at the second bandwidth and receives at the first bandwidth. The transceivers are equipped with antennas providing beam divergence small enough to ensure efficient spatial and directional partitioning of the data channels so that an almost unlimited number of transceivers will be able to simultaneously use the same spectrum. Antennas and rigid support towers are described to maintain beam directional stability to less than one-half the half-power beam width. In a preferred embodiment the first and second spectral ranges are 92.3-93.2 GHz and 94.1-95.0 GHz and the half power beam width is about 0.36 degrees or less. In this preferred embodiment the Ethernet network is a Gigabit Ethernet providing data communication among switch banks at 1 gigabits per second and communication among a large number of users at 100 Mbps
In the above and other preferred embodiments the digital service links utilize off-the-shelf Ethernet equipment. In a preferred embodiment a remote located luxury hotel provides 100 Mbps data rate communication for its guests in each of its rooms. In another embodiment high speed digital data service is provided to more than 100 workspaces. The service is provided quickly and costs far less than a fiber optic installation would cost.